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What does the drug AOD-9604, which has been used by some Australian football players, actually do? And is it safe to use?

Recently, controversy has erupted over Australian football players using the drug AOD-9604.

Initially developed as an 'anti-obesity' drug, AOD-9604 is widely marketed online as a drug that can burn fat and build muscle mass.

But Professor Gary Wittert, a leading authority in obesity management at the University of Adelaide, says there's no evidence in humans that AOD-9604 is effective for burning fat or building muscle mass.

"I cannot understand why athletes are taking it," he says.

Wittert is concerned about what is on the public record about the drug, adding: "There's so much misinformation out there."

AOD-9604 is a modified fragment of human growth hormone that was originally developed by Professor Frank Ng at Monash University in Australia in the 1990s, says Wittert.

He says the idea was to find a drug that could have the catabolic (fat-busting) effects of human growth hormone, without its (muscle-building) anabolic effects.

Wittert says he has led five out of the six studies on AOD-9604 carried out in humans, including a six-month study, funded by Metabolic Pharmaceuticals, the company that developed the drug.

"This showed quite clearly there was no effect on weight," he says.

"It was never going to be an anti-obesity drug."

Wittert says there's an explanation for why the drug doesn't work in humans despite showing some impact in mice.

"In mouse studies, AOD-9604 was shown to break down fat and prevent weight gain, but it was also shown that this effect over the longer term was dependent on a specific receptor," he says.

"When you give AOD-9604 to mice that are deficient in this receptor the weight-losing effect is lost."

"It's not surprising that AOD-9604 doesn't work in humans because the receptor on which it appears to be dependent is not the same in mice and humans."

Despite some anecdotal reports that it can build muscle, Wittert says he has been unable to find any data to support this.

Indeed, he says, the drug was specifically designed not to have anabolic effects.

Unlike human growth hormone, AOD-9604 does not stimulate the production of IGF1 (Insulin-like Growth Factor 1), which is involved in growth and development, says Wittert.

"It's designed not to have an effect on muscle," he says.

In a statement released earlier this year, Metabolic's parent company Calzada says the obesity program was abandoned in 2007 as trials did not show "a clinically meaningful weight loss outcome across the trial population."